1. Field of the Invention
This invention relates to a gas diffusion semiconductor electrode and solar cell and a process for gaseous fixation, such as nitrogen photoreduction. In one embodiment, the solar cell has a gas diffusion photosensitive cathode with p-type semiconductor material on the surface of a porous matrix diffusion layer in contact with an electrolyte and forming one side of a flowing liquid electrolyte chamber, the opposing side of the electrolyte chamber being formed by an anode through which light may pass for the illumination of the p-type semiconductor photocathode. The electrolyte is capable of providing ionic conductance between the cathode and anode and an external electrical circuit between the cathode and anode completes the circuit and has a power source capable of providing a bias voltage to the p-type semiconductor material. Nitrogen may be reduced to ammonia or hydrazine by passing a nitrogen containing gas through a porous matrix diffusion layer of the gas diffusion photosensitive cathode while the p-type semiconductor is illuminated.
2. Description of the Prior Art
Fixation of nitrogen by combination with oxygen has been effected by use of the electric arc as a source of energy as taught by U.S. Pat. No. 2,134,206 and by means of high energy ionizing radiation to irradiate a catalytic bed as taught by U.S. Pat. No. 3,378,475.
Photoreduction of nitrogen to produce ammonia and hydrazine has received considerable recent attention. The fixation-reduction of molecular nitrogen promoted under mild conditions in solution by lower valent titanium using alkali metal or naphthalene radical anion as a reducing agent has been described in the references E. E. van Tamelen, G. Boche, S. W. Ela, and R. B. Feehter, J. Am. Chem. Soc., 89, 5707 (1967); E. E. van Tamelen, and M. A. Schwartz, ibid., 87, 3277 (1975); and E. E. van Tamelen, G. Boche and R. Greeley, ibid., 90, 1677 (1968). Electrolytic reduction of molecular nitrogen to the ammonia level utilizing a titanium coordinating species in an aluminum chloride electrolyte is taught by E. E. van Tamelen, Bjorn Akermark, ibid., "Electrolytic Reduction of Molecular Nitrogen" pps. 4492-4493 (1968). The catalytic effect of titanium in the electrolytic reduction of nitrogen in a titanium-aluminum system is described in E. E. van Tamelen, Douglas A. Seeley, "The Catalytic Fixation of Molecular Nitrogen by Electrolytic and Chemical Reduction", ibid., 91, 5194 (1969). Reduction of molecular nitrogen to ammonia and hydrazine by reaction of sulfuric acid with tungsten and molybdenum complexes is taught by J. Chatt, A. J. Pearman, R. L. Richards, "The Reduction of Mono-Coordinated Molecular Nitrogen to Ammonia in a Protic Environment", Nature, 253, 39-40 (1975).
Photolysis of water and photoreduction of nitrogen on titanium dioxide doped with iron in a catalyst bed is described in G. N. Schrauzer, T. D. Guth, "Photolysis of Water and Photoreduction of Nitrogen on Titanium Dioxide", J. Am. Chem. Soc., 99, 7189-7193 (1977); G. N. Schrauzer, "Prototype Solar Cell Used in Ammonia Process", C & E N, 19-20, (Oct. 3, 1977). Photo enhanced reduction of nitrogen on p-GaP electrodes using an aluminum anode and a non-aqueous electrolyte in a galvanic cell is taught by C. R. Dickson, A. J. Nozik, "Nitrogen Fixation via Photoenhanced Reduction on p-GaP Electrodes", J. Am. Chem. Soc., 100, 8007-8009 (1978). One disadvantage of the described system is that aluminum is consumed in its function as a reducing agent.